The Mystery of Flying Honeydew: A Strange Case of Unabashed Thievery

Yesterday I introduced the amazing lantern bugs and their fast-flying honeydew. I mentioned that ants, animals that often collect honeydew from homopteran insects, were unable to enjoy it because of the speed with which the honeydew drops were expelled. And yet, when Kenji and I started investigating the behavior of lantern bugs in a systematic fashion we quickly discovered that ants had found a way of tapping into this source of food after all, and they weren’t very nice about it.

As we cataloged various kinds of insects that were coming to catch a few sweet drops from the lantern bugs, often we would see large, light colored snails near these insects. But surely these snails couldn’t have anything to do with the bugs, right? We decided to look into this strange observation in more detail, and what we found was quite surprising. First of all, the snail, Euglandina aurantiaca, is a predator, feeding mostly on other snails. Still, there they were, politely tapping the bugs with their tentacles, and expertly catching flying droplets of honeydew. To be able to catch the liquid, the snail formed a hood over the tip of the insect’s abdomen with its head and foot, and eventually the honeydew would accumulate on its ventral surface, allowing the snail to drink it. Why would a predaceous snail want honeydew in the first place? It appears that, in addition to the benefit of getting some high quality carbohydrates, the phloem of the tree species that the lantern bugs particularly like, Simarouba amara, contains pretty high levels of calcium, the element that snails need to grow their shells.

We also noticed that whenever we saw the snails, and often even before they showed up, ants of the genus Camponotus(a yet undescribed, new to science species) would gather near the lantern bug, waiting for something. First, they gingerly approached the tip of the bug’s abdomen, but never attempted to catch the honeydew. But as soon as the snail came and started collecting the flying liquid, the ants (usually one or two individuals) ran up the snail’s head and started drinking the honeydew off its foot.The snails, of course, were not too happy about it and tried to (slowly) shake them off and, in the end, the botheration by ants usually drove the snails away.

“Can I help you with something?” – Once the snail is covered with honeydew, the ant climbs its head and begins to drink it; this thieving behavior is known as kleptotrophobiosis. [Canon 1Ds MkII, Canon 100mm macro, 2 speedlights Canon 580EX]

Kenji and I described our observations (J. Nat. Hist. 2007, 41: 37-40) and classified the ants’ behavior as kleptotrophobiosis – feeding by stealing food from others. This kind behavior is not very common in the animal kingdom, but you can find its examples in several groups: frigate birds steal fish in flight from other marine birds, hyenas steal the kill from leopards, and small, kleptoparasitic spiders feed on prey caught in the web of large Nephila orb weavers. But ants stealing food from a slow snail take this behavior to a new low – they’d better think twice before lecturing that poor grasshopper again!

This was my first qcuestion when I saw the snails with the fulgorids: what compound were they interested in? Turns out, it was probably calcium. Like you, I have wondered what the source of calcium in rainforest is. But many plants sequester calcium from the soil, and animals have learned to tap into it.

I absolutely love these posts! As a natural sciences curatorial trainee, working with the lantern bug collection at the Manchester Museum was one of the highlights for me. I couldn’t stop telling everyone how amazing Fulgoridae are.